Computer networking involves the linking of computers, peripheral devices, and perhaps telephonic devices, into a consolidated data communications system. Technological networking advances are taking place at various networking levels, including multi-node network structures such as multipoint, star, ring, loop and mesh network topologies used in networks ranging from local area networks (LAN) to proliferative global area networks (GAN) such as the Internet. Of great consequence to the continued success of computer networking is the ability to efficiently and economically interconnect these various networks in local and remote configurations.
As networks continue to gain acceptance and favor, there is a continuing desire to transmit ever-increasing amounts of data across the transmission medium in a given amount of time. In other words, the increased demand for network solutions has propelled the need to maximize the data bandwidth. This need has led to many techniques and systems for increasing the data bandwidth, such as the use of T-carrier services (e.g., Tl and T3), and integrated services digital networks (ISDN).
Emerging applications for higher speed communications applications have driven the need for advanced technologies that leverage the installed base of communications platforms around the world. One such technology allows relatively high-speed data transmission over existing copper-based twisted-pair lines. This technology, referred to as digital subscriber line (DSL) technology, includes various species, including high-bit-rate DSL (HDSL), very high-bit-rate (VHDSL), and asymmetric DSL (ADSL). These various types of digital subscriber line technologies are generically referred to as "xDSL" technologies. Each of these technologies allows digital information to be transferred from a service provider, via the existing copper telephone lines, at rates as high as 6 megabits/sec (Mbps). Typically, an ADSL line can provide rates near 6 Mbps downstream from a service provider, and 384 Kbps upstream to the provider using the existing telephone line. As can be seen, these data rates far exceed many competing technologies (ISDN: 128 Kbps, T1: 1.544 Mbps, etc.). These higher digital connectivity data rates are being demanded by users for Internet access, telecommuting, video conferencing, and the like.
ADSL often uses one of two modulation schemes, including discrete multi-tone (DMT) and carrierless amplitude-phase (CAP) modulation. DMT is a technology that divides the available carrier frequency bandwidth of a channel into multiple bandwidth sections. Each of these sections is "characterized" for noise and attenuation. After the characteristics of the channel are known, the transmitters and receivers can compensate for the deficiencies in the transmission path. A carrier tone within each of the channels (i.e., bandwidth sections) is used for transferring the data bits. A frequency "band" includes a group of contiguous bandwidth sections, where deficient bands receive fewer data bits to transmit than do more operable bands. The aggregate effect of this carrier frequency channelization is higher data bandwidth over the channel.
CAP modulation is also an out-of-band modulation technique. CAP modulation attempts to equalize the line using digital techniques, by learning the channel characteristics, and applying the inverse of those characteristics on the receiving side of the channel. The net effect of this equalization is to provide a more ideal channel response.
The significance of the use of the existing telephony copper base should not be underestimated. The undepreciated world-wide value of this asset has been estimated at over 600 billion dollars. There are approximately 700 million local loops around the world, and over 160 million of these are in the United States. It would therefore be desirable to utilize this pre-installed communications base, as physical connectivity costs would be greatly reduced.
Connections by individual computer users to networks such as the Internet has grown at astronomical rates. Moreover, surveys have indicated that many Internet subscribers have more than one computer at a local site, and it appears this trend will continue. Therefore, it is also becoming more common to connect small office/home office (SOHO) computers and other devices into a local network configuration within the SOHO environment.
The aforementioned xDSL techniques have been applied to connect external information systems to subscriber nodes. However, in order to connect computing devices into a local network, most of the available interconnection technologies require the user to install additional cabling. While XDSL techniques have been used to transmit data across existing copper twisted-pair telephone lines in a remote networking configuration, they have not been used in a local environment using a common transmission medium and a common modulation technique while allowing local network communications to be distinguished from remote communication transfers.
The present invention provides a solution to these and other shortcomings of the prior art, and provides other advantages over the prior art.